Chemists, microbiologists, and other scientists, as well as businesses and universities, spend a great deal of time and money in the search for chemical compounds which possess herbicidal, pesticidal, or microbicidal activity. Unfortunately, this search for new control agents often proceeds very slowly and cannot keep up with the demands of agriculture, veterinary medicine, and human medicine. One reason the process of identifying and isolating control agents does not move forward more rapidly is that there has been a lack of a dependable, predictable procedure which could be followed in order to arrive at the desired control agents.
Problems which have been encountered in the search for control agents for microbial plant pathogens are typical of the roadblocks researchers in other fields have encountered in their search for control agents. The development of new bactericides suited to the control of plant disease has been minimal during the past 25 years (1983 Resolution of the American Phytopathological Society). Effective agricultural chemicals that are environmentally compatible, preferably systemic, and that are not harmful to humans or animals are high priority needs in agriculture.
Only a few products are available within the area of antimicrobials for plant disease control, and these have very serious limitations. Streptomycin (which is now in use for seed treatment) is plagued with regulatory problems. Also, development of resistance to streptomycin is a problem, as is its unsatisfactory spectrum of activity. Treatment with copper is ineffective, in part due to phytotoxicity.
Similarly, in the search for herbicidal compounds, researchers have not been able to keep up with the demands of agriculture. Even though many effective control agents are available and on the market, new resistant strains of weeds frequently necessitate the development of new herbicides.
The isolation, identification, and synthesis of new herbicides often proceeds slowly even where herbicides have previously existed for the target weed. This inability to produce new herbicides is due, in part, to a general lack of understanding as to how previous herbicides functioned. Traditionally, herbicides and many other pesticides have been isolated by following large-scale screening procedures. These procedures essentially involve treating target weeds with a tremendous variety of chemical compounds until a compound which kills or otherwise controls the plant is found.
The use of screening procedures to obtain control agents has at least three distinct disadvantages. First, it is largely trial and error. Thus it is difficult to determine when and if success will be achieved, and, therefore, a great deal of time and money can be wasted testing compounds which have no control properties, and which do not help lead the researchers toward a useful control agent. The second major drawback of screening procedures is that these procedures may not give researchers any information regarding how close they are to identifying an effective control agent. For example, the researcher may be testing a compound which does not show control properties but which would be an effective control agent if a simple chemical modification of the compound were made.
Finally, even when screening procedures are successful in identifying a control agent, often the researcher initially has very little, if any, idea as to how the newly found chemical compound exerts its herbicidal, pesticidal, or bactericidal effect. Therefore, significant research aimed at elucidating the mode of action of a new control agent is often required before additional related control agents can be identified.
The subject invention is a systematic process for identifying and producing herbicides, pesticides, and bactericides. The process focuses on the production of chemical agents which will disrupt the metabolism of the target weed, microbe, or pest. The use of antimetabolite compounds as control agents is not new. However, to the extent that antimetabolite agents have been used in medicine and agriculture in the past, they have been selected using inefficient screening procedures. The process disclosed herein has several important advantages over the "brute-strength" approach which has been used in the past. In particular, the disclosed process provides a scientific, predictable, means for identifying, isolating, and synthesizing new pesticides, herbicides, bactericides, and derivatives thereof. Advantageously, and unlike the traditional screening procedures, the disclosed method does not depend upon every property needed by the successful compound to be correct initially.
If a compound displays evidence of being an effective inhibitor but does not inhibit pure cultures of phytopathogen or does not work in the field, this does not mean that the compound must be abandoned as a possible control agent. Instead, the compound can be modified in an appropriate way to optimize that compound's pesticidal, herbicidal, or bactericidal properties. This is in contrast to screening where valuable compounds can be missed because some modifiable factor is not just right.